Guides
The paperwork, explained properly.
Written for people doing the job, not for search engines. If a guide doesn't tell you something you can act on, it shouldn't be here.
What legally has to be on a UK invoice
The actual list, split into what every invoice needs and what only VAT-registered businesses need.
How to number invoices without painting yourself into a corner
Sequential, unique, and no gaps. The schemes that survive contact with a busy year, and the ones that do not.